A kingpin is used to connect a trailer to a towing tractor. More particularly, the tractor carries a bearing like plate called a fifth wheel which has a slot. The kingpin includes a cylindrical base, a cylindrical shank and a cylindrical head, all of which extend through the floor of the trailer and engage the slot so that the tractor and trailer are coupled together. Thousands or tens of thousands of present coupling arrangements use a kingpin having a shank of a certain dimension.
An anti-jackknife assembly has been developed for tractor trailers. However to utilize such anti-jackknife assembly requires, for some applications, a kingpin with a shank dimension of greater diameter than the diameter of the kingpin in current use in those tractor trailers. To merely replace the smaller diameter kingpins with the larger diameter kingpins would require the removal of the welded in place kingpin and subsequent replacement, a costly, time consuming and labor intensive operation. The present invention solves the problem by resizing and enlarging the kingpin in situ without the requirement for removing it.